Drum assemblies with preformed inserts

ABSTRACT

A plastic drum assembly includes a preformed insert fused to at least a portion of the corner of the drum. In order to facilitate lifting and handling the drum, the insert is formed with a pair of indentations on opposite sides of a ridge. The method involves placing the preformed plastic insert across at least a portion of a corner of a mold cavity and blow molding the drum in the cavity to form the drum and fuse the drum corner to the insert. The disclosure also is concerned with methods for forming indentations in a blow molded plastic drum and with a method of reinforcing the corner of a blow molded drum.

This is a division of application Ser. No. 787,153 filed Apr. 13, 1977.

BACKGROUND OF THE INVENTION

This invention relates to plastic drums and drum assemblies, preformedplastic inserts for use in plastic drum assemblies, and methods offorming plastic drums and plastic drum assemblies.

Steel and fiber drums have long been utilized for the shipment andstorage of liquid, paste, powder, and solid products. A fundamentalrequirement of all such drums is the need for safe and convenienthandling. For this purpose, a number of specialized devices have beendeveloped including fork-lift trucks which can grasp the drum around itscenter girth or by other means. One such means which is widely used isthe "parrot's beak" mechanism; this device includes a pair of jaws whichengage a structure on the steel lid and locking band of such drums. Morerecently, plastic drums blow molded from high density polyethylene havebecome popular. These drums have rounded corners at the ends, and suchcorners and the slick surface of the polyethylene plastic make thehandling of these drums very difficult. It is not feasible to apply the"parrot's beak" jaws to the top rim of such a plastic drum due to theabsence of a suitable structure to be engaged by the jaws of the"parrot's beak." This has led to a number of attempts to modify theplastic drum construction to accommodate the " parrot's beak" jaws. Anumber of these prior art expedients will be discussed more fullyhereinafter with reference to the drawings. It will be noted here,however, that the most promising of the prior art expedients involvesthe provision of a preformed plastic insert fused to the corner of thedrum with the insert surmounted on the normal drum structure. This isaccomplished by altering the conventional mold cavity used for blowmolding the plastic drum; a groove is cut through the corner of the moldcavity wall for holding the preformed plastic insert. However, thisprocedure unduly complicates the design, construction and operation ofthe metal mold.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide improvedplastic drum assemblies which overcome the aforesaid drawbacks. Inparticular, it is an object of the present invention to provide a methodof forming a plastic drum assembly fused to a preformed plastic insertto facilitate lifting the drum which does not require modification ofthe conventional plastic drum mold.

Further objects of the invention include the provision of preformedplastic inserts particularly suitable for these ends, an improved methodof forming the plastic drum assemblies, an improved method ofreinforcing the corners of blow molded plastic drums, and improvedmethods of forming indentations in the walls of blow molded plasticdrums.

Briefly, the invention contemplates the provision of a blow moldedplastic drum assembly, at least a portion of the upper corner of whichis modified and joined to a preformed plastic insert having a pair ofindentations on opposite sides of a ridge to facilitate lifting the drumassembly. This preformed plastic insert includes a base having opposededge surfaces which are flush with the surface of the upper end of thedrum and the cylindrical surface of the side wall of the drum. One sideof the base is fused to the modified corner portion of the blow moldeddrum, while the aforementioned ridge extends outwardly from the oppositeside of the base. The crown of the ridge may be convex, concave, orflat. Because of the requirements of the method, the insert is sodimensioned that it does not extend upwardly or outwardly beyond theusual contours of the drum corner. In one embodiment, the insert isformed so as to drain any water which might collect in the upperindentation.

The method of forming the drum assembly involves placing the preformedinsert within an unmodified conventional mold for blow molding plasticdrums with the side edges of the base engaged respectively with an endwall and a side wall of the mold cavity completely to close off at leasta portion of the corner of the mold cavity. The crown of the ridge ofthe insert may engage or, in other embodiments, may extend just short ofthe corner of the mold cavity. After the insert is positioned within themold cavity, a plastic parison is blow molded into the mold cavity toform the drum assembly with the modified corner structure fused to thebase of the insert. In order to enhance the fit of the insert with themold cavity and provide heat bonding between the insert and the blowmolded material, the insert is preheated throughout the part before itis placed in the mold cavity. In an embodiment of the method, supportmembers may be engaged in the indentations of the plastic insert toprevent the plastic insert from collapsing during the blow moldingprocess.

It also is contemplated that a blow molded drum be reinforced by placinga preformed reinforcing member in the corner of the mold cavity tobecome fused to the corner of the blow molded drum during the blowmolding process. In another aspect of the invention, a blow molded drumis provided with one or more indentations by omitting the plastic insertand leaving one, or both, of the support members in the mold cavity.

These and other objects, features, and advantages of the invention willbecome more readily apparent from consideration of the followingdetailed description of preferred embodiments of the invention whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing two drum assemblies of theinvention mounted on two different types of drum handling equipment;

FIG. 2A is a partial schematic section view of an example of a drum ofthe prior art;

FIG. 2B is a partial schematic section view of another example of a drumof the prior art;

FIG. 3 is a partial section view showing the normal corner configurationof a plastic drum;

FIG. 4 is a partial schematic section view of an additional example of adrum;

FIG. 5 is a partial schematic section view of a drum embodiment of theinvention;

FIG. 6 is a partial schematic section view of a drum assembly of theprior art;

FIG. 7 is a partial schematic section view showing a step in the methodof making the prior art embodiment of FIG. 6;

FIG. 8 is a partial schematic section view showing a step in a preferredmethod of making a drum assembly of the invention;

FIG. 9 is a partial schematic section view of a preferred embodiment ofa drum assembly of the invention engaged by a "parrot's beak" mechanism;

FIG. 10 is a partial schematic section view of the same embodiment shownin FIG. 9 engaged by a finger;

FIG. 11 is a front elevation view of the preferred drum assembly of theinvention as shown in FIGS. 9 and 10;

FIG. 12A is a partial schematic section view of a corner reinforcementassembly of the invention;

FIG. 12B is a partial schematic section view illustrating a method ofmaking the corner reinforcement assembly of FIG. 12A;

FIG. 13 is a plan view of a preferred embodiment of an insert of theinvention;

FIG. 14 is a partial plan view of a drum assembly of the inventionemploying the insert of FIG. 13;

FIG. 15A is a schematic section view taken along line 15A--15A of FIG.13;

FIG. 15B is a schematic section view taken along line 15B--15B of FIG.13;

FIG. 15C is a schematic section view taken along line 15C--15C of FIG.13;

FIG. 15D is a schematic section view taken along line 15D--15D of FIG.13;

FIG. 15E is a schematic section view taken along line 15E--15E of FIG.13;

FIG. 16 is a plan view of a second preferred embodiment of insert of theinvention;

FIG. 17 is a partial plan view of a drum assembly of the inventionemploying the insert of FIG. 16;

FIG. 18A is a schematic section view on line 18A--18A of FIG. 17;

FIG. 18B is a schematic section view on line 18B--18B of FIG. 17;

FIG. 18C is a schematic section view on line 18C--18C of FIG. 17:

FIG. 18D is a schematic section view on line 18D--18D of FIG. 17;

FIG. 18E is a schematic section view on line 18E--18E of FIG. 17;

FIG. 18F is a schematic section view on line 18F--18F of FIG. 17;

FIG. 19 is a partial schematic section view of a further embodiment of adrum assembly of the invention;

FIG. 20 is a partial schematic section view showing a step in apreferred method of the invention;

FIG. 20A is a partial schematic section view corresponding to FIG. 20illustrating a problem faced in the method of FIG. 20;

FIG. 21 is a partial schematic section view illustrating a modifiedmethod step of the invention;

FIG. 22 is a partial schematic section view illustrating anotherembodiment of the method of the invention;

FIG. 22A is a partial elevation view showing the structure of a drummade by the method of FIG. 22;

FIG. 23 is a partial schematic section view illustrating a furthermodification of the method of FIG. 20;

FIG. 24 is a partial schematic section view illustrating yet anothermethod of the invention;

FIG. 24A is a partial schematic section view of a drum made by themethod of FIG. 24;

FIG. 25 is a partial schematic section view illustrating still anothermethod of the invention; and

FIG. 25A is a partial schematic section view of a drum made by themethod of FIG. 25.

DETAILED DESCRIPTION

A pair of drum assemblies 200 of the invention are shown in FIG. 1, eachbeing carried by a different type of drum handling apparatus. As will beexplained more fully hereinafter, each drum includes a preformed plasticinsert 210 having a pair of indentations on opposite sides of a corner.The drums are otherwise conventional and include a cylindrical side wall201, an end wall 202, a pair of rolling hoops 206 and 207, and closures208 and 209 for openings in the top end wall 202. As seen at the leftside of FIG. 1, a "parrot's beak" mechanism 110 is engaged with a drumassembly 200. This mechanism includes a pair of opposed grabbing andlifting jaws which are engaged respectively, in the indentations. The"parrot's beak" mechanism is mounted on a carriage 113 from which a drumengaging leg 114 projects to engage with the side wall 201 at a pointbelow lower rolling hoop 207. On the right-hand side of FIG. 1, anothertype of drum handling apparatus 115 is shown. This apparatus is mountedon a pair of wheels 116 and includes a pair of drum engaging arms 117for engaging opposed points on the cylindrical side wall 201 of the drumassembly 200. A hook 118 extends from a point near the end of apparatus115 to engage with the upper indentation of preformed insert 210.

Before continuing with a detailed description of the embodiment of theinvention as shown in FIG. 1, it will be well to review the practices ofthe prior art. For many years, steel and fiber drums have been used forthe shipment and storage of thousands of different liquid, paste,powder, and solid products. A fundamental requirement of all such drumsis the need for safe and convenient handling, such as lifting, rolling,and sliding, normally accomplished by hand or other means of graspingand transporting the drums individually or in groups. For this purpose,many special attachments have been devised for fork-lift trucks and thelike for grasping the drum around its side wall or for otherwiseengaging the drum. A very popular attachment is referred to in the drumhandling art as a "parrot's beak" mechanism and typically includes apair of pivoted jaws for engaging a special structure provided on thecorner of the drum. In FIG. 2A, a "parrot's beak" mechanism 110 includesjaws 111 and 112 engaged with a special top rim structure 101 of a steeldrum 100. In operation, bottom jaw 112 applies a vertical force F₁ tothe under side of rim 101; and top jaw 111 applies a lateral force F₂ tothe inside surface of rim 101. FIG. 2B illustrates the use of the"parrot's beak" jaws mechanism 110 with a steel or fiber drum 120provided with a steel lid 121. A special rim is formed by rolling overthe upper edge 122 of drum 120, by rolling the peripheral edge 123 oflid 121 over rim 122, and by applying a locking band 124 over the rolledover peripheral edge 123. This special structure is engaged by the jaws111 and 112 as shown in FIG. 2B.

Plastic drums which are blow molded from high density polyethylene arenow widely used and typically are provided in the 55-gallon size. Asshown in FIG. 3, such a drum 130 is provided with a rounded corner 131at both ends. Such a smooth shape and the slick surface of thepolyethylene plastic make the handling of these drums very difficult. Itis not feasible to apply the "parrot's beak" jaws to a round corner suchas the corner 131. Accordingly, the utility of plastic drums has beenseriously limited; such drums, in their usual configuration, cannot beused by that segment of drum users who require the use of a "parrot'sbeak" lifting and handling device. For this reason, a number of attemptshave been made to modify the plastic drum construction to accommodatethe "parrot's beak" jaws. It has been suggested, for example, to blowmold the drum 140 with a special corner configuration 141. Although thiscorner configuration may then be engaged by the jaws 111 and 112 of the"parrot's beak" mechanism, the corner will not be strong enough tosupport the drum; the plastic has a lower stiffness and tensile strengththan steel. There is also a tendency in a blow molded drum for thethickness t to be reduced at the corner 131 (see FIG. 3). When thecorner of the drum is configured as illustrated in FIG. 4, there is aneven greater tendency for the plastic at corner configuration 141 tothin out, making the corner even weaker.

The applicant has had some success with a blow molded drum configurationas shown in FIG. 5. Here, the drum 150 has a top wall 151 and acylindrical side wall 152. A pair of indentations 154 and 156 are formedin the top and side walls, respectively, after the drum has been moldedby applying a heated tool at the portion 153 of top wall 151 and theportion 155 of side wall 152, thus forming indentations 154 and 156. Thecorner configuration 157 will then be engagable by the jaws 111 and 112of the "parrot's beak" mechanism as illustrated in FIG. 5. With thisconstruction, it has been found that the dimension X₁ should bemaintained at less than approximately 3/8 inch. When this dimension isused, a full drum can be lifted and handled successfully with the"parrot's beak" mechanism. When so engaged by jaws 111 and 112, the twoindentations 154 and 156 are pushed toward each other to the deflectedpositions 154' and 156' shown by phantom line to meet at point X₂. Ifthe distance X₁ is greater than approximately 3/8 inch, it has beenfound that one of the jaws 111 and 112 is liable to push through theindentation, thereby causing a leak in the drum. Although approximately5/8 inch is the correct maximum distance for X₁ for 55-gallon drums withan average wall thickness of about 0.25 inch, a different maximumdistance may be appropriate for drums of different size, wall thicknessor loading factor. In any case, the maximum distance should be selectedso that the indentations contact before development of a shearing force.It has been found that the post-forming operation done by hand isprohibitive for cost reasons. This post-forming could also beaccomplished automatically by first blow molding a drum in theconfiguration shown in FIG. 3 and then projecting special top and sideforming pieces from the walls of the mold cavity into the hot plasticbefore the plastic has frozen. However, the cost of modifying the moldin this way also is prohibitive. A less costly method of forming theindentations is shown in FIG. 25, which will be described more fullyhereinafter.

Another technique, suggested in the prior art, for modifying the cornerof a blow molded drum is shown in FIG. 6. The drum 160 has a top wall162 and a cylindrical side wall 161 connected by the usual roundedcorner 163. A special preformed polyethylene insert 164 is surmounted onand heat sealed or cemented to corner 163. Insert 164 includes anupstanding rim 165 and a shoulder 166 which are engagable, respectively,by the jaws 111 and 112 of the "parrot's beak" mechanism. As before, jaw111 engages the inside surface of rim 165 with a lateral force F₂, whilejaw 112 engages the shoulder 166 with a vertical force F₁. Grippingforce vectors F_(X) and F_(Y) are generated, as shown in the figure.

The preformed insert 164 of FIG. 6 may be attached to a blow molded drumin the manner shown in FIG. 7 which illustrates the technique of heatsealing the insert in the mold. It is necessary to modify the mold 168by cutting a recess 169 through the corner of the mold to receive thepreformed insert with its surface to be joined to the blow molded drumconforming exactly with the normal corner configuration of the drum.Polyethylene is then blow molded into the mold cavity and the blowmolding pressure pushes the hot polyethylene against the exposed surfaceof insert 164. This causes the blow molded corner of drum 160 to becomefused to the exposed surface of insert 164, which surface will have beenpreheated. The result is a heat sealed insert 164 bonded to the corner163 of a blow molded drum 160. In order to make it possible to placeinsert 164 in recess 169 and to remove the drum and fused-on insert fromthe mold upon completion of the blow molding cycle, the mold must beseparated along the line of separation 168'. This technique has theobvious drawback of complicating the design, construction, and operationof the metal mold.

This problem is avoided by the present invention, an embodiment of whichis specifically illustrated in FIG. 8. Here, the mold 220 is theconventional mold used for blow molding plastic drums having the usualcurved corner configuration as illustrated in FIG. 3. The mold 220 has acylindrical side wall 221 and a generally flat end wall 222, these beingconnected by a curved corner 223. A special preformed polyethyleneinsert 210 is placed in the mold cavity to close off the portion of themold cavity containing the corner 223. Insert 210 includes a generallyflat base 211 having flat side edges 212 and 213 which are angled sothat they may be positioned flush with the top wall 222 and side wall221, respectively, of the mold. Insert 210 is formed with a pair ofindentations 214 and 215 on opposite sides of a protruding ridge 216. Inthe embodiment shown in FIG. 8, the crown 217 of ridge 216 is convex andhas the same radius of curvature as the corner 223 of the mold and, infact, is engaged with this corner. As will be explained hereinafter, itis also possible to use inserts, the ridge of which is spaced from thiscorner. Hot polyethylene is introduced into the mold and blow moldedunder blow molding pressure to form a drum 200 with a cylindrical sidewall 201 formed by side wall 221 of the mold and a top wall 202 formedby top wall 222 of the mold. The corner 203 of the drum is deformed bythe base 211 of insert 210 and becomes heat sealed to the insert alongthe interface formed on the exposed side of base 211. As will beexplained more fully hereinafter, preferred embodiments of insert 210extend only partially about the periphery of the drum and, therefore,close off only a portion of the corner 223 of the mold. In that case itis necessary that the entire periphery of the insert, including edges212, 213, and corresponding end edges, be engaged snugly with the wallsof the mold cavity to prevent hot polyethylene from leaking into thecorner. As will be evident from FIG. 8, the inclusion of the preformedinjection molded insert 210 in contact with the mold, and the closingoff of a corner of the mold, eliminates any requirement for any majormodifications to the mold itself. When, however, the insert is placed inthe top of the mold, as shown in FIG. 8, it is necessary to providesuitable holding devices to retain the insert in position. This can beavoided by molding the drum upside down, as is shown in FIG. 20. Gravitywill then hold the insert in place. Thus, drums can be modified inaccordance with the present invention without costly modification oralteration of the standard drum mold merely by placing a perfumedinjection molded insert into the appropriate corner of the mold. Afterthis, the blow molding process proceeds in the usual manner.

A drum assembly 200 formed in accordance with the method shown in FIG. 8as illustrated in FIG. 9. The blow molded drum has a cylindrical sidewall 201 and a generally planar top wall 202, these being connected atselected portions of the corner by a modified corner configuration 203.This corner configuration is heat sealed to the base 211 of preformedplastic insert 210 which presents a pair of indentations 214 and 215 onopposite sides of ridge 216. These indentations are engaged by the jaws111 and 112 of the "parrot's beak" mechanism, there being a verticallifting force F₁ applied by jaw 112 to the lower side of ridge 216 and alateral force F₂ applied to the other side of ridge 216 by jaw 111. Inaddition to the forces F₁ and F₂ which are applied to insert 210 by jaws111 and 112, the jaw mechanism (not shown) operates to increase thegripping forces (analogous to the forces F_(X) and F_(Y) applied in theprior embodiment of FIG. 6) as the vertical force F₁ increases, thusincreasing the gripping force as the weight of the drum increases. Itwill be noted that these gripping forces, by virtue of the placement ofindentations 214 and 216, will not be along the same vertical line as inthe case in the embodiment of the prior art shown in FIG. 6.

When a steel drum, as illustrated in FIG. 2A or FIG. 2B, or a plasticdrum with a shaped "grabbing" corner, as illustrated in FIG. 4 or FIG.5, fails as a result of overloading, the forces applied by the jaws 111and 112 cause a leakage opening to be formed in the wall of the drum.If, on the other hand, a drum of the present invention employing apreformed plastic insert 210 fails as a result of overloading, theplastic insert fractures, but a leakage opening does not form. Thus, thedrum can continue in service; it can be re-handled at another locationon the plastic insert or by engaging the other, unfractured, insert.

Although FIG. 9 illustrates the use of a drum assembly of the presentinvention with a "parrot's beak" drum handling mechanism, it will beobserved from FIG. 10 that the indentations 214 and 215 are also usefulfor manual handling of the drum. Thus, in FIG. 10, a finger 225 isengaged in indentation 215 to apply a tipping force for manually tippingthe drum. In actual practice, the fingers of one or two hands may beengaged in indentation 215, thus making it a simple matter to tip androll the drum manually.

It will also be observed that the upper indentation 214 is useful withdrum handling apparatus as shown at the right-hand side of FIG. 1. Thusa hook 118 engages in this upper indentation. For this purpose, it is ofparticular utility to dimension insert 210 to place indentation 214 nomore than approximately 1/2 inch from the edge of the drum. Since thiswill require a reach of only 1/2 inch, any standard hand truck is usefulwith a drum assembly of the present invention.

As previously observed, an important advantage of the present inventionis the elimination of minimum thickness problems which normally occur inthe corners of blow molded drums. This is shown in FIG. 3. For example,a typical blow molded 55-gallon drum has an average thickness ofapproximately 0.25 inch with a minimum thickness (usually in the cornerof the drum) of approximately half that value. The addition of thepreformed injection molded insert of the present invention substantiallyincreases this minimum thickness in two ways. First, the addition of athickness s (see FIG. 10) inherent in the preformed injection moldedpiece is added to the normal thickness of the corner of the blow moldeddrum wall. Second, the tendency for the blow molded drum to thin out ina corner is substantially reduced so that the thickness t (see FIG. 10)is greater than the corresponding thickness obtained at the normalrounded corner as illustrated in FIG. 3.

As seen in FIG. 11, a complete drum assembly 200 of the inventionincludes cylindrical side wall 201 and generally flat top wall 202. Anarcuate corner 204 extends between the side and top walls, and a similararcuate corner 205 extends between the cylindrical side wall and agenerally flat bottom wall. Conventional rolling hoops 206 and 207 areprovided on side wall 201, and a boss 208 surrounds in opening to thedrum. In accordance with teachings of the present invention, a preformedplastic insert 210 is shown fused to a modified corner configuration 203at the top of the drum.

Drum assembly 200 will most usually be provided in the 55-gallon size.When this drum is lifted by the "parrot's beak" mechanism, it will besubjected to a number of forces. These include the force F_(W)representing the combined weight of the drum and its contents, F₁representing the lifting force provided by the lower jaw of the"parrot's beak" mechanism, F₂ representing the lateral force provided bythe upper jaw of the "parrot's beak" mechanism against the preformedplastic insert, and F_(S) representing a force acting on the side of thedrum. F_(W) will, in a typical application, be about 500 lbs. Since F₁overcomes the weight of the drum and its contents, F₁ will be equal toF_(W), which, as previously stated, will be approximately equal to 500lbs. in a typical application. The summation of vertical forces ΣF_(Y)will, therefore, be equal to 0 (F₁ -F_(W) =O). As indicated in FIG. 11,lateral force line F₂ is approximately 23 inches above the center ofrolling hoop 207 corresponding to the location of force F_(S). Thecenter of drum assembly 200 is 6 inches above the center of rolling hoop207 and force F_(S) and 17 inches below the location of force F₂.Moreover, vertical lifting force F₁ is applied to a point which is 11inches from the vertical axis of the drum. By virtue of the moment armscreated by the forces at the distances indicated, it follows that F_(S)will be equal to 11/23 F₁. Thus, when F₁ is equal to about 500 lbs.,F_(S) will be equal to approximately 240 lbs. The sum of the momentsoperating on the drum assembly, Σ moments, will be equal to 0, since 23F_(S) will be equal to 11 F₁. F₂ counterbalances F_(S) ; thus F₂ will beequal to F_(S) (which, as indicated above, is equal approximately to 240lbs.). The sum of lateral forces ΣF_(X) will be equal to 0, since F₂-F_(S) will be equal to 0.

As indicated above with reference to FIG. 3, there is a tendency of thecorners of a blow molded plastic drum to thin out. It is thereforedesirable to stiffen the corners of the drum so as to permit rolling ofthe drum without crushing. The increase in stiffness is achieved, asshown in FIG. 12A, by the addition of a pair of preformed plasticreinforcements 232 to the lower corner 231 of a blow molded drum 200,extending between the side wall 201 and the bottom wall 230 of the drum.Like preformed inserts 210, preformed inserts 232, which may beinjection molded of high density polyethylene plastic, are arcuate, eachoccupying approximately 85° at each side of the bottom of the drum.Preferably, the inserts 210 are centered at 90° from the parting line,which extends across a diameter of the drum and corresponds to the edgesof the mold halves. The corner of the blow molded drum is normallythinnest, and thus in the greatest need for reinforcement, at thispoint, because the greatest percentage of "draw" occurs at the corner atthis angular distance from the parting line. This problem is usuallydealt with by "programming" the parison (the extended tube of moltenplastic from which the drum is formed) by thickening the ends of theparison in order to locate more material at the otherwise thin portionsof the corner. This, unfortunately, also locates an excess of materialin adjacent areas which are already too thick. The need for programmingthe parison is minimized, or even eliminated, by using preformed arcuateinserts 232 according to the invention. The portion of the insert isthickest near the transverse center of the corner and at the upper andlower edges is thinnest. Since the arcuate ceter of the insert iscoincident with the point (90° from the parting line) which is thinnest,the insert is designed so that it is thickest at its arcuate center andthinnest at its ends. The insert may be formed in a properly designedinjection mold or by vacuum forming a constant thickness plastic sheetonto a male mold. The method of fusing preformed plastic reinforcement232 to the plastic corner 231 is illustrated in FIG. 12B. The mold 240has a mold cavity shaped to form the conventional blow molded plasticdrum. Preformed reinforcement insert 232 is shaped to fit within thecorner of the mold cavity. When the plastic drum 200 is blow molded intothe mold cavity it will conform to the walls of the mold cavity and tothe exposed surface of preformed reinforcement insert 232 to which itwill become fused. As before, it is desirable to preheat preformedreinforcement insert 232 to enhance the fusion between insert 232 andthe corner 231 of the blow molded drum. By providing preformedreinforcement insert 232, it is relatively easy to achieve the minimumthickness in the corner required by certain regulations, withoutproviding an excess of thickness in those parts of the drum where theadditional thickness contributes nothing functional to drum performance.

Preformed plastic insert 210 will now be considered in more detail. Thisinsert is shown in plan view in FIG. 13 and is shown in a top plan viewof a drum assembly fused to the drum in FIG. 14. A number of sectionviews of the insert are found in FIGS. 15A, 15B, 15C, 15D, and 15E. Asis most readily apparent from FIGS. 13 and 14, insert 210 is arcuate,having the same radius of curvature along side edge 213 as the drum towhich it will be fused. The insert extends only partially about theperiphery of the drum and, in a typical embodiment, each of two insertsfused to the drum at opposite sides thereof will cover 85° of arc. As isapparent from FIG. 15A, the insert includes side edges 212 and 213 whichare angled to be flush with the upper and side walls, respectively, ofthe drum. A ridge 216 protrudes from the center of the base andterminates in a convex crown 217. A pair of indentations 214 and 215 lieon opposite sides of ridge 216. These indentations and ridge 216 extendfor most of the length of insert 210, but the ends of the insert areformed with uninterrupted curved surfaces 218 and 219. Turning,specifically, to the section views, it will be noted from FIG. 15A,which represents the cross section of the insert over most of itslength, that indentations 214 and 215 undercut ridge 216. The crown 217is convex, generally following the shape of the usual cornerconfiguration 242 of the drum. Crown 217 is spaced slightly inwardlyfrom the usual corner configuration 242. In a typical practical exaple,the radius of curvature of the curved portion of the usual cornerconfiguration 242 is 1.02 inch, while the radius of curvature of crown217 is 1.0 inch to provide a clearance between crown 217 and the cornerof the mold of the order of 0.01-0.02 inch. As was noted above, however,it is also possible to dimension crown 217 so as to fit within andengage the corner of the mold. The base 211 of the insert has a surfacewhich appears generally flat in cross section on the bottom side of theinsert opposite to the side from which ridge 216 protrudes. As the endsof the insert are approached, the bottom side of the insert movesprogressively closer to the normal corner configuration 242. Ridge 216and indentation 215 disappear at the point reached in FIG. 15C; andindentation 14 disappears at the point reached in FIG. 15D. The surfaceof insert 210 becomes curved surface 219 (or 218 at the other end), andthe insert continues to diminish in thickness as shown in FIG. 15E.

As viewed in FIG. 15A, a typical practical embodiment will be 11/8 inchin width and height between the acute corners of base 211. Base 211 willbe 0.15 inch thick. Ridge 216 will have a height to the center of crown217 of 23/32 inch. As viewed in FIG. 14 installed on the drum, the innercorner of edge 212 has a radius of 10.0 inches, and the outer edge ofthe insert at edge 213 has a radius of 11.625 inches.

A second preferred embodiment of preformed plastic insert is shown at310 in FIGS. 16 and 17, depicting the insert respectively in plan viewand in plan view as installed on a drum 200. The preformed plasticinsert 310, which again is injection molded of high density polyethylenplastic, includes a base 311 having a bottom surface which is relativelyflat as seen in section and edges 312 and 313 which, respectively, areplaced flush in the mold to engage an end wall of the mold cavity and aside wall of the mold cavity so that these edges are flush with the topwall of the drum assembly and the cylindrical side wall of the drumassembly. A ridge 316 extends from the top side of base 311. A firstindentation 314 undercuts one side of ridge 316; a second indentation315 on the opposite side of ridge 316 undercuts the other isde thereof.

In practising the method of the present invention, the preformed plasticinsert is preheated throughout the part before it is placed in the mold.This is desirable because there is inevitably some warpage in thepreformed insert; and it is, thus, difficult to obtain good conformationbetween the preformed plastic insert and the walls of the mold cavity.This problem is overcome by preheating throughout the part, since, inthat event, a warped preformed injection molded part is less rigid andthus will conform to the mold under pressure. Thus, the preheatingoffers a synergistic effect by allowing the slightly distorted injectionmolded insert to conform to the contour of the blow mold and, at thesame time, to achieve a temperature (210°-240° F.) sufficient to insuregood fusion and bond with the blow molded plastic which is pressedagainst the insert by blow mold pressure. An additional advantage of thepreheating of the insert prior to its placement in the blow mold is theability of the insert to conform to a mold of somewhat greater orsmaller body radius.

When the insert 210 is preformed in an injection molding process, theplastic material is injected into a metal mold at an elevatedtemperature and held under pressure. As the cold metal of the moldchills the insert during the cooling process, the "skin" of the insertfreezes while the interior of the insert is still in a hot viscousstate. Thus, as the rounded skin at 217 freezes and hardens, the insidematerial cools less rapidly and is still soft. As the inside slowlycools, it shrinks. However, the rounded surface, as it freezes, is rigidand thus cannot shrink inwardly. For this reason, the shrinkage of theinside material will tend to form vacuum voids which may constitute weakspots. This can be avoided by providing a flat crown, or even an inwarddepression, for the ridge. Although frozen and rigid, the flat surfaceor an inward depression can bend inwardly as the inside material coolsand shrinks, thus avoiding the formation of voids. Thus, in theembodiment of FIGS. 16, 17, and 18A, a flat crown 317 is provided onridge 316 of insert 310.

It will be readily apparent that when the embodiment of FIG. 14 isplaced out-of doors in the rain there will be a tendency for water tocollect in pper indentation 214. This can be a nuisance when the drum istipped as it is handled. This problem is substantially avoided by theembodiment of FIGS. 16 and 17. The ends of insert 310 are configued soas to permit water collecting in indentation 314 to drain as indicatedby the arrows in FIGS. 16 and 17. This is made possible by providing atransition section 319 between the ends of the insert 320 and theprotruding ridge 316. There is also a transition between indentation 315and end cavities 321 through raised ribs 318.

The configuration of insert 310 for these purposes will be bestunderstood by consideration of the various section views. Turning firstto FIG. 18A, it will be noted that the normal corner configuration ofthe drum is indicated in phantom line at 300. Protruding ridge 316extends just short of this configuration and, as was discussed above,presents a flat crown 317 to the corner. The side edges 312 and 313 ofthe base 311 are flush, respectively, with the top and side walls of thedrum. FIG. 18B shows the transition from the normal configuration ofFIG. 18A to the end configuration of the insert. Here, indentation 315has evolved into a lateral rib 318, while indentation 314 continues. InFIG. 18C, the bottom of insert 310 begins to approach line 300; ridgesection 319 separates indentation 314 from end cavity 321. In FIG. 18D,the height of the ridge section 319 diminishes, while indentation 314and cavity 321 are maintained. In FIG. 18E, ridge section 319 is muchsmaller, as indentation 314 and cavity 321 become much shallower.Finally, in FIG. 18F, a relatively thin end structure 320 is shown.Since end structure 320 and ridge section 319 do not wall off the endsof the upper indentation to the same extent as the ends of insert 210,water does not accumulate therein, but tends to drain over ridge section319 as indicated by the arrows in FIGS. 16 and 17.

The dimensions of insert 310 are generally the same as the dimensions ofinsert 210. Again, 85° of arc define the length of arcuate insert 310.The inner edge 312 is on a radius of curvature of 10.0 inches, and theouter edge 313 is on a radius of curvature of 11.625 inches. The heightand width of the insert as seen in FIG. 18A is 11/8 inch. Ridge 316 fitswithin the usual corner configuration 300 which, as before, has a radiusof 1.02 inches. The width of ridge 316 at its base is approximately 5/8inch. The length of insert 310 as viewed in FIG. 16 is 141/4 inches, andits arcuate length is approximately 151/4 inches.

The drum assembly embodiments discussed above are closed drums in whichthe top wall of the drum is integral with the side walls thereof. It isalso possible to apply the principles of the present invention to anopen ended drum. This is illustrated in FIG. 19, where drum assembly 400includes a cylindrical side wall 401, and an upper corner 402 upon whicha preformed plastic insert 410 is surmounted. Unlike the preformedinserts 210 and 310, discussed hereinabove, preformed insert 410, whichis also injection molded of high density polyethylene, is annular andextends completely about the periphery of the drum. Insert 410 includesa base 411 having edges 412 and 413 which are angled to fit flush withthe corresponding walls of the mold cavity so as to seal off a corner ofthe mold. A pair of indentations 414 and 415 are provided on oppositesides of a ridge 416 protruding from one side of base 411. Ridge 416terminates in a flat crown 417.

In forming drum assembly 400, preformed insert 410 is placed in the topcorner of a conventional plastic drum mold cavity with edges 412 and 413sealing off the corner of the mold. As already explained, insert 410 isannular and, thus, extends completely around the corner of the moldcavity. Crown 417 will be spaced inwardly from the corner. The plasticparison is the introduced into the mold cavity and blow molded to engagethe side and end walls of the cavity and to form corner 402 whichconforms to the shape of the bottom side of base 411 of insert 410. Asbefore, insert 410 is preheated throughout the part before it is placedin the mold and, therefore, a good fusion is obtained between corner 402and the base 411 of the insert. As indicated in phantom line, a top wall403 is also formed. This wall, however, is removed by cutting on aradius R along cutline 420 to provide the top opening in the drum.

A lid 421 which may be molded from plastic or formed from steel is thenprovided. This lid includes an annular recess 422 the outer side ofwhich engages against the cut edge of corner 402. It is formed with anannular ridge 423 extending over edge 412 of the insert and is thenprovided with an annular recess 424 which is engaged in indentation 414of insert 410. The lid has another ridge 425 which extends over theupper corner of ridge 416 and a generally flat annular surface 426extending over flat crown 417. Finally, the outer periphery of lid 421includes a bent portion 427 extending over the lower corner of ridge416. It will be observed that a rubber gasket 430 is provided betweenthe upper corner of ridge 416 and the inside of ridge 425 of lid 421. Inorder to maintain lid 421 on the drum assembly, a locking ring 432 isprovided. This locking ring includes an upper arm 433 which engagesagainst ridge 425 of the lid and a lower arm 434 which is received inindentation 415 of preformed insert 410. As will be observed from FIG.19, a "parrot's beak" mechanism may become engaged with drum assembly400 with upper jaw 111 being received in annular recess 424 of lid 421and lower jaw 112 being received against lower arm 434 of locking ring432 in recess 415. By applying lateral and vertical forces as previouslyexplained, the "parrot's beak" mechanism will then operate to lift drumassembly 400 which is filled as indicated at 405.

Although FIG. 19 illustrates the use of a "parrot's beak" mechanism withdrum assembly 400 with lid 421 applied, it is to be understood that the"parrot's beak" mechanism may also be used with an open drum with lid421 removed. In that case the jaws 111 and 112 of the "parrot's beak"mechanism will become engaged, respectively, in indentations 414 and 415of insert 410.

The embodiment of FIG. 19 has substantial advantages over prior art openheaded plastic drum designs. These prior art designs include blow moldedchimes which tend to become distorted when drums are stacked. Thiscauses the gasket to leak. In addition, there is a tendency for the topopening to ovalize. The embodiment of FIG. 19 avoids these problems,because performed insert 410 adds rigidity without making the upper partof the drum especially heavy.

As was explained above, the method of joining the preformed plasticinsert to the drum includes the step of preheating the insert throughoutthe part before it is placed in the mold; this insures that the insert,which may be warped, will fit snugly across the corner of the mold andalso insures that there will be a good heat seal between the modifiedcorner of the drum and the facing surface of the base of the insert.Referring to FIG. 20, it will be seen that a preheated insert 210 isplaced in the lower corner 223 of mold 220. This illustrates the usualpractice of blow molding the closed head drum upside down. By moldingthe drum upside down, the need to provide means in the corner of themold to retain the prewarmed insert during the blow molding step isavoided. Gravity holds the preformed insert in place. It may, therefore,be placed simply in the mold by hand. The figure otherwise correspondsto FIG. 8. Insert 210 is preheated to a temperature in the range210°-240° F., which is usually just under the melting point of thethermoplastic used to form the insert. This provides good heat sealbonding with the blow molded material 203 of the corner of the drumwhich hits the inside surface of the insert and fuses thereto under thepressure of blow molding. The pressure of the blow molding will forcethe softened insert to conform snugly with the corner of the mold. Itshould be borne in mind that the step, according to the presentinvention, of preheating the insert throughout the part to provideflexibility for good conformity to the corner of the mold differssignificantly from the prior art practice of heating an insert at thecontact surface only while leaving the remainder relatively cool.

One problem with a preheated insert, which is heated throughout thepart, is the tendency of the insert, in the event that it isoversoftened, to deform under blow molding pressure. This is illustratedin FIG. 20A where a typical blow molding pressure of 100 lbs. per sq.in. is applied and is shown deforming the portions of base 211 whichborder on indentations 214 and 215. This tendency to deform the insertcan be avoided in the manner shown in FIG. 21. A metal support member440 may be attached to the side wall of mold 220 so as to receiveindentation 215. A second metal support member 441 is shaped to snapinto indentation 214 before it is placed within the mold. Thus, apreheated insert 210 with support member 441 snapped into indentation214 is placed in the corner of the mold by fitting indentation 215 oversupport member 440. When blow molding pressure is now applied, base 211will be firmly supported by support members 440 and 441 and will notdeform. It also is possible to fasten both support members to the mold.In that event, however, it is necessary to shorten and round off theapex of the support member extending into the indentation 214 or 215 topermit removal of the finished drum from the mold without "hanging up"on support members 440 and 441. Even though these members will beabbreviated and not in full contact with the surface of the respectiveindentation of the insert, enough support will be provided to preventcollapse of the base 211 of the insert under pressure. Another variationinvolves leaving both support members unattached to the mold. For this,support member 440 should assume the same configuration as supportmember 441. Both support members would be snapped into the respectiveindentation 214 or 215 before the inset is placed in the mold, and bothsupport members would be removed with the drum after forming.

As shown in FIG. 22, it has been found that a support member 440', theapex of which is rounded off, may be used alone to shape a blow moldeddrum. Thus, a blow molded drum 450 is formed in mold 220 with anindentation 451 formed adjacent the corner of the drum by support member440'. A drum made in accordance with the method illustrated in FIG. 22is shown in FIG. 22A. A finger receiving recess 451 is provided justbelow the corner of drum 450 and is useful for manually handling thedrum.

It is also possible to employ one support member only in the forming ofa drum assembly. This is shown in FIG. 23 where metal support member 441is snapped into recess 214 before it is placed in the mold corner.Although support member 440 has been omitted, it has been found that, insome cases, support member 441 is sufficient to provide the necessarysupport for the insert as the drum is molded.

As shown in FIG. 24, a drum may be shaped by employing support member441 only. The support member is attached to an end wall of the moldcavity. Drum 460 is then blow molded with support member 441 formingrecess 461. The shrinkage of the drum wall in the vertical direction hasbeen found to be sufficient to clear the indentation 461 from thesupport member 441 so that the finished drum can be removed from themold without interference. The drum 460 made by the method of FIG. 24 isshown in FIG. 24A. The recess 461 is positioned between the top wall 463of drum 460 and the usual curved corner 462. This recess 461 is usefulfor engagement by the hook 465 of a hand truck.

As shown in FIG. 25, a pair of recesses may be provided in a blow moldeddrum by employing both support member 440 and support member 441.Support member 440 is secured to the side wall of mold 220, whilesupport member 441 is secured to a moveable mold section 220' in the endwall thereof. Plastic drum 470 is then blow molded into the mold cavity.Support member 440 will then form recess 471, and support member 441will form recess 472 on opposite sides of the arcuate corner 473 of thedrum. In order to remove the formed drum from the mold, one side of mold220 must be moved laterally away from the drum. Since support member 441would block such separation of the mold from the drum, it is necessaryfirst to retract support member 441. To this end, mold section 220' isretracted by the actuation, for example, of a hydraulic piston (notshown) to move support member 441 completely below the end wall of mold220. The drum made by the method shown in FIG. 25 is illustrated in FIG.25A. Drum 470 includes a recess 471 and a recess 472 on opposite sidesof corner 473. These recesses are engaged respectively by jaws 111 and112 of a "parrot's beak" mechanism. As will be readily apparent, themethod of FIG. 25 may serve as an alternative method for forming thedrum illustrated in FIG. 5. Accordingly, the spacing betweenindentations 471 and 472 should correspond to the rules prescribed forthe spacing between indentations 154 and 156 of FIG. 5.

Although the invention has been described with reference to plasticdrums having arcuate, or round, corners between the end walls and thecylindrical side wall, it will be recognized that the principles of theinvention are also applicable to drums having other configurations.Preformed plastic inserts may be used, for example, with drums havingsquare corners. In that case, portions of the square corners will bemodified by the insert as the drum is blow molded. Inserts of theinvention may also be applied to drums which are square or rectangular.In these cases, the preformed insert will no longer be arcuate, butrather, will be straight so as to conform with the straight walls of thedrum.

As indicated above, preferred embodiments of drum assemblies accordingto the invention involve preformed plastic inserts which are heat sealedto a modified corner of a blow molded drum. It is to be recognized,however, that it is also broadly within the purview of the invention tosecure a preformed insert to a pre-modified drum corner by otherconventional securing methods and means, such as by induction welding,epoxy cement or screws.

In this specification, the term "parrot's beak" has been used todescribe a mechanism of the prior art employing grabbing and liftingjaws for engaging cooperating means provided at the top rim of the drum.

As has been demonstrated, the principles of the present invention avoidthe major drawbacks of prior art methods employing preformed inserts.Unlike the prior art methods, which require major modification ofexisting conventional blow molding molds, it is merely necessaryaccording to the present invention to set a preformed plastic insert inthe corner of the mold cavity with the peripheral edge of the insertsealing off the corner. It will be recognized that this makes itpossible rapidly to changeover the use of the mold to or from the blowmolding of conventional plastic drums and the blow molding of plasticdrum assemblies according to the present invention.

While preferred embodiments of the invention have been shown anddescribed, it will be apparent to those skilled in the art that changesand modifications can be made without departing from the spirit of theinvention, the scope of which is defined in the following claims.

The invention claimed is:
 1. A preformed insert adapted to be joined toa corner structure of a plastic drum to facilitate lifting thereof andadapted to be positioned within an arcuate corner of a conventional blowmold for forming said drum, said blow mold having an end wall, a sidewall, and said arcuate corner connecting said end wall and side wall,said insert comprising: a relatively broad base, a relatively narrowridge extending from one side of said base, and a pair of indentationsrespectively on opposite sides of said ridge extending lengthwise of theridge, said base having a continuous peripheral edge and beingdimensioned to fit across said arcuate corner of said mold with saidridge extending outwardly towards, and no further than, said arcuatecorner and with said continuous peripheral edge of said base incontinuous engagement with said mold to seal off at least a portion ofsaid corner of said mold as plastic parison is blow molded in said moldand keep said plastic parison from entering said indentations.
 2. Aninsert as recited in claim 1, wherein the crown of said ridge is convex.3. An insert as recited in claim 1, wherein the crown of said ridge isflat.
 4. An insert as recited in claim 1, wherein said insert is arcuateto fit partially about the periphery of said drum.
 5. An insert asrecited in claim 1, wherein the ends of said ridge are shaped to permitwater to drain from one of said indentations.
 6. An insert as recited inclaim 1, wherein said insert is circular to extend entirely about theperiphery of said drum.
 7. An insert as recited in claim 1, wherein saidbase has edge surfaces contiguous with said continuous peripheral edge,said edge surfaces being adapted to engage flush with said top and sidewalls, respectively, of the mold.
 8. An insert as recited in claim 1,wherein said insert is formed of high density polyethylene.
 9. An insertas recited in claim 1, wherein the crown of said ridge is convex and hasthe same radius of curvature as said arcuate corner of said mold andextends outwardly to engage said arcuate corner when said insert ispositioned in said mold.
 10. An insert as recited in claim 1, whereinthe crown of said ridge is convex and has substantially the same radiusof curvature as said arcuate corner of said mold and extends outwardlyjust short of engagement with said arcuate corner when said insert ispositioned in said mold.